Rhythmical Pulsation in Scyphomeduse. 129 
It is, then, evident that the relative powers of the inhibitors in sea- 
water are from strongest to weakest—magnesium, calcium, and potassium. 
Indeed, the stimulating effect of the sodium chloride in the sea-water is 
exactly offset by the subduing tendency of the magnesium, calcium, and 
potassium ; and thus it is that the sea-water as a whole neither stimulates nor 
inhibits the pulsation of the jelly-fish. The sea-water is, indeed, a delicately 
Fic. 12.—Test of relative inhibiting power of magnesium, calcium, and 
potassium of sea-water. 
balanced fluid in all respects, for it contains poisons and antidotes which 
exactly counteract one the other. 
The pulsation-stimulus is evidently not derived directly from the sea- 
water, but is engendered within the sense-organs of the bell-margin. 
Experiments show that the sense-organs can not maintain pulsation unless 
they be immersed in a fluid containing calcium in solution. Indeed they 
must constantly be supplied with calcium. On the other hand the pulsation- 
stimulus once it leaves the sense-organs and travels through the diffuse 
nervous network of the subumbrella is relatively independent of the amount 
of calcium in solution, for such a wave may endure for more than two hours 
if traveling through subumbrella tissue, whereas the sense-organs can not 
continue to send forth pulsation-stimuli for more than 6 to 10 minutes in a 
solution which lacks calcium, but contains all the other elements of sea-water. 
We are now in a position to state that each pulsation is due to a nervous 
stimulus that originates somehow in the sense-organs. The question is how 
does it originate? 
In all of the Scyphomedusz the mar- fe 
ginal sense-organs are little clubs, the ‘ oe 
hollow entodermal cores of which con- 
tain a terminal mass of concretionary 
crystals. It has been commonly supposed 
that these crystals are composed of cal- 
cium carbonate, but I find that they are 4, 13.—Median section of marginal 
actually calcium oxalate with a certain sense-organ of Cassiopea xamachana. 
e : ‘ ect., ectoderm; ent., entoderm; o0c., 
small proportion of urea and uric acid. ocellus; of., concretionary crystals. 
In nitric and hydrochloric acids they dis- 
solve slowly without evolution of gas, but in sulphuric acid they slowly give 
off bubbles of carbon dioxide. In short, they respond to all of the chemical 
tests for oxalates. 
